The dissident Cuban blogger Yoani Sánchez – famed for her outspoken online critiques of the country's communist regime – has issued an appeal to Brazil's president, Dilma Rousseff, to help her leave the Caribbean island.

Sánchez, a Havana-based writer who has been accused by Cuban authorities of conducting a "cyberwar" against the government, has not been able to leave the country since 2004 because of migration rules that require Cubans to receive government permission to travel.

She has now been invited to the Brazilian state of Bahia in February for the screening of a documentary about press freedom in Cuba and Honduras in which she features.

But speaking to the Brazilian television channel Record this week, Sánchez said she expected her latest request for an exit permit would again be declined without "high-level intervention".

Sánchez told Record she had "exhausted all of the options inside my country to get them to allow me to travel".

In the video appeal to Rousseff, posted on YouTube, Sánchez called on Brazil's first female president to intervene.

"Please help me," said the blogger, who says it is her 19th attempt to get travel permission from Cuban authorities. "Through this small video I want to send a very respectful [and] very humble message … to the president of Brazil, Dilma Rousseff."

"Unfortunately I am forbidden from leaving my own country – I have not committed any crime."

Referring to the time Rousseff spent in jail during Brazil's military dictatorship, Sánchez said: "I know very well that she has felt first hand … what excessive control and repression is."

"I have done everything that is within my reach but the wall of control, the wall of censorship, the wall which stops me travelling freely and returning to my island seems not to move," said Sánchez, whose supporters have also created an online petition calling on Rousseff to intervene.

Before Christmas, activists had hoped that Cuba's president, Raúl Castro, would announce major changes to the country's migration laws, particularly the rule that means Cubans require exit permits to travel abroad.

But while Castro, who officially took over from his brother as president in 2008, announced pardons for nearly 3,000 prisoners, those hoping for a loosening of travel rules were disappointed.

"The migration reforms … were not announced again," Sánchez says in her video appeal to Rousseff. "In the 21st century … we are forbidden from leaving and entering freely our country."

Sánchez has earned international plaudits for her blog, Generación Y, on which she publishes regular critiques of the Cuban authorities, often secretively posted from internet cafes.

In 2008, Time magazine named her one of the world's 100 most influential people. The magazine's profile, written by the American novelist Oscar Hijuelos, described her "feisty dedication to the truth".

"Under the nose of a regime that has never tolerated dissent, Sánchez has practiced what paper-bound journalists in her country cannot: freedom of speech," Hijuelos wrote.

"Opening the world's eyes to the real Cuba … no longer requires a wire service dispatch; it can be done with a cell phone," she wrote.

Meanwhile, Cuban authorities have vented their anger at a Twitter user whom they accused of starting a wave of online rumours this week claiming that the former president, Fidel Castro, had died.

An article posted on the state-run Cubadebate website pointed the finger of blame at a tweeter called @Naroh.

In the story, entitled: "New lie against #FidelCastro fails on Twitter", the website claimed that after the rumours began "necrophiliac counterrevolutionaries, aided by some media, immediately started to party." Responding to the allegations that he had started the hoax, Naroh tweeted: "Cuba is blaming me for killing Fidel Castro on Twitter. Can I now consider myself a Twit-star?"